1. Field of the Invention
The present invention relates to improvements in a reclining device with which a seat back is controllably adjustable in its inclined position relative to a seat cushion by effectively using a planetary gear mechanism.
2. Description of the Prior Art
It is well known that a vehicular seat is provided with a reclining device between a seat cushion and a seat back. The seat back is inclinably attached to the seat cushion through the reclining device. With this arrangement, the vehicular seat is freely adjustable in its position so as to fit with a passenger.
A reclining device of this kind requires the following: A structure is simplified; An assembly operation is easily carried out; A seat back is o freely adjustable in a proper position; A control operation is carried out by small power and with no play; And a sufficient rigidity can be gained so as to support the weight of the passenger by the seat back.
In view of these points, a variety of devices have hitherto been proposed and put into practical use. One of them is an arrangement with which a seat back is smoothly and inclinably adjustable in its position by effectively using a plurality of planetary gears. Such reclining devices are disclosed, for example, in Japanese Utility Model Publication No. 58-26602 and Japanese Utility Model Provisional Publication Nos. 60-187645 and 60-187646. In this arrangement, a plurality of planetary gears are supported on a predetermined revolution orbit in a state of engaging with internal gears of the base and arm frames which have a difference in number of teeth. A control gear engaging with the planetary gears is rotatably supported on an axis of a control shaft. Therefore, the arm frame is inclinably adjusted relative to the base frame by the rotation of the control shaft.
However, the following difficulties have been encountered in the above-discussed reclining device: Since the control gear is made of sheet metal or the like in general, a play tends to occur between the planetary gears and the control gear, and it is difficult to gain a sufficient strength with this device. Therefore, it is difficult that the arm frame is rigidly supported by the reclining device. In particular, when an electric motor is used for the power source to drive the device, a large torque is applied to the control gear through the rotation shaft. This causes the control gear to be broken and to slip out from the rotation shaft.
In general, since the supporting plate made of sheet metal is formed in a star shape, the supporting plate receives a part of each planetary gear at an edge section of the supporting plate and is loosely supported on the rotation shaft. Therefore, a play occurs between each of the planetary gears or rotation shaft and the other part. This prevents the device from obtaining a sufficient supporting strength and a rigid fixed state.
With the above-mentioned device, since the planetary gears unequally apply the pressing force to the supporting plate in the centripetal direction, the rotation shaft is eccentrically supported in the shaft-hole of the base frame and the arm frame. This makes the rotation shaft to be rotated with some difficulties.
In case that the device is driven by the electric motor or the like, since a large torque is applied to the gears of the reclining device, it is required that the gears have a sufficient mechanical strength so as to have a high reliability.